This invention relates to the use of blends of syndiotactic and isotactic poly-xcex1-olefin to achieve an overall reduction of the coefficient of friction of films made from such blends. This may also be viewed as a reduction of characteristics or enhancement of xe2x80x9cslipxe2x80x9d characteristics of the films without inclusion of excessive additives, other than poly-xcex1-olefins, into the polymer, its films, or other articles of the polymer.
It is known that films of polyolefins may have tendencies toward sticking to themselves or displaying coefficients of friction which are higher than desirable. With these tendencies to stick to itself or have low coefficient of friction, such films may become difficult to use and handle. Slip agents are available in the marketplace, these include fatty amides such as erucamide, fluoropolymers including Viton(copyright), and various other agents, including some anti-block agents which may assist in enhancing the apparent slip or coefficient of friction of films or articles.
While these additives are beneficial in reducing the coefficient of friction for polymer films, compounders will prefer not to add too much of them to the polymer or during film production in light of costs and since film characteristics may be adversely affected. Also, inclusion of large amounts of such additives may yield films having other detrimental characteristics such as transfer of additive smells or tastes into goods enclosed within the film products, particularly foods or medicines.
We have found that these additives may be kept at reasonable levels while providing films with good coefficients of friction by blending polymers of differing stereoregular configurations. From this, what appears to be a synergistic effect between the slip additive and the syndiotactic polyolefin provides advantage.
Others have found benefit in blending polymers to enhance different characteristics. U.S. Pat. No. 4,857,409 issued Aug. 15, 1989 to Hazelton and Shulman, describes a composite film composition comprising a rubber core layer wherein said layer is comprised of about 50 to 85 weight percent rubber and 15 to 40 weight, percent of a polyolefin and a minimum of one polyolefin resin skin layer coextruded onto said core layer. The rubber component of the core layer is selected from a group of specific possibilities.
U.S. Pat. No. 4,500,681 issued Feb. 19, 1985 to Shulman describes a composition of matter comprised of a thermoplastic elastomeric blend of a polyolefin component, an isobutylene-backbone elastomer component, and a copolymer component of ethylene and an unsaturated ester of a lower carboxylic acid. The polyolefin component comprises from about 20 to about 65 weight percent of the composition and is selected from isotactic polypropylene or polypropylene reactor copolymer containing about 1 to 20 weight percent of an alpha-olefin comonomer or mixtures thereof. The isobutylene-backbone elastomer component comprises from about 20 to 60 weight percent of the compound and the copolymer component comprises about 7 to about 40 weight percent of the composition.
These blended polymer resins do not provide the tough film with reduced coefficient of friction as is addressed by our invention.
Our invention provides, at least, polymer blends which yield films having reduced coefficient of friction over similar films which contain higher loadings of slip agents or similar loadings with no syndiotactic poly-xcex1-olefin additive. Also provided are films of reduced coefficients of friction and methods for producing such blends and such films.